1. Field of the Invention
The invention is related to the field of communications, and in particular, to providing access to IMS networks and IMS services using legacy devices.
2. Statement of the Problem
As set forth in the 3rd Generation Partnership Project (3GPP), an IP Multimedia Subsystem (IMS) provides a common core network having access-agnostic network architecture for converged networks. Service providers are accepting this architecture in next generation network evolution. The IMS architecture is initially defined by the 3GPP to provide multimedia services to mobile subscribers over an IP network. IP networks have become the most cost savings bearer network to transmit video, voice, and data. IMS uses the advantage of IP networks to provide multimedia services for IMS subscribers on an IMS platform. The signaling used within IMS networks is SIP protocol. IMS defines the standard SIP interface between application servers, the IMS core network (CSCF), the IMS subscriber, the IMS database (HSS), and IMS billing elements. These standards can reduce the network integration costs and let the subscriber enjoy more stable services.
On the IMS platform, the traditional supplementary services, such as call forwarding, conferencing, and call waiting could be available for IMS subscribers. Also, many new data services, such as instant messaging, video calls, video on wait, and web-based services, will also be available for the IMS subscribers.
An IMS subscriber uses an IMS device to access the IMS network and its associated IMS services over the IP network. Before the IMS services are available to the IMS subscriber, the IMS subscriber needs to register with the IMS network through the IMS device. The registration provides many functions in the IMS network, such as authenticating the subscriber, determining the services available to the subscriber, etc. The registration procedure is according to IMS standards. Thus, IMS-compliant devices are able to register with the IMS network to receive IMS services.
One problem with IMS networks as currently defined by the 3GPP is that legacy devices, such as traditional telephones, that do not register with the IMS networks are not able to access the IMS networks and IMS services. There are many legacy devices being used for communication that are not able to register with an IMS network. One type of legacy device is an H.323 IP device. H.323 IP devices do perform some registration when accessing a network, but the registration is not compliant with IMS standards. Another type of legacy device is a traditional telephone using the Public Switched Telephone Network (PSTN). Traditional phones are circuit-based and do not register with a network before use. There is currently no effective way for legacy devices to register with and access IMS networks and IMS services.